A schematic diagram of a steam power plant is shown in figure 1. In a simple steam power plant, at the top of the boiler high-pressure superheated steam leaves the steam drum, also referred to as a steam generator and enters the turbine. In the turbine, steam expands and in doing so does work, which enables the turbine to drive the electric generator. The steam, now at low pressure, exits the turbine and enters the heat exchanger, where heat is transferred from the steam to the cooling water. Since a large amount of cooling water is required, power plants are generally built near rivers or lakes, leading to thermal pollution of those water supplies. More recently, condenser cooling water has been recycled by evaporating a fraction of the water in large cooling towers, thereby cooling the remainder of the water that remains as a liquid. In the power plant shown in figure 1, the steam power plants are generally designed to recycle the condenser cooling water by using the heated water for district space heating.
The pressure of the condensate leaving the condenser is increased in the pump, enabling it to return to the steam generator for reuse. In many cases, an economizer or water preheater is used in the steam cycle and in many power plants, the air is used for combustion of the fuel may be preheated by the exhaust combustion product gases. These exhaust gases need to be purified before releasing into to the environment, so there are wide number of complications to the simple steam power plant cycle.
Figure 2 is a photograph of the power station plant located in Esbjerg, Denmark. The tall buildings shown at the center is the boiler house, next to which are buildings housing the turbine and other components. Also noted are the tall chimney, or stack, and the coal supply ship at the dock. This power station plant has set a world record for efficiency, converting 45% of the 850 MW energy generated consumption into electric power. Another 47% of energy is reusable for the district space heating, an amount that in older plants was simply released to the environment, providing no benefit.
The steam power plant described utilizes coal as the fuel for combustion. Other power plant stations use natural gas, fuel oil, or biomass as the fuel. Many power plants operate on the heat released from nuclear reactions instead of fuel combustion.